CN113985174B - Open-circuit fault diagnosis method for power device of three-phase converter - Google Patents

Abstract

The invention discloses a method for diagnosing an open-circuit fault of a power device of a three-phase converter. First, a model predictive control is used for the three-phase converter to obtain the optimal switch state S _a1 S _b1 S _c1 of the converter at the time (k+1); then, the voltage between the midpoint of each phase and the ground is detected to obtain the switch state S _a2 S _b2 S _c2 of the converter in actual application; further, according to the fault characteristics of the converter power device under the open-circuit condition, the difference between S _a1 S _b1 S _c1 and S _a2 S _b2 S _c2 is compared, and a power device open-circuit fault flag signal FT _n is set; finally, according to the states of different fault flag signals, it is determined whether the power device has an open-circuit fault, thereby realizing the diagnosis and positioning of the open-circuit fault of the power device of the three-phase converter. The method realizes the online diagnosis of the open-circuit fault of the power device of the three-phase converter, has a significant effect on the simultaneous faults of single-tube, double-tube and multi-tube, is simple and easy to implement, and can effectively reduce the loss caused by the open-circuit fault of the converter power device in the motor controller.

Description

A method for diagnosing open circuit faults of power devices in three-phase converters

Technical Field

The invention relates to a method for diagnosing open-circuit faults of power devices of a three-phase converter, which can be applied to converter fault diagnosis.

Background Art

With the continuous development of energy technology, new energy vehicles have gradually become an important part of the automobile market with their many advantages such as energy saving, environmental protection, and high efficiency. Compared with traditional internal combustion engine vehicles, new energy electric vehicles are "zero pollution" vehicles, do not emit exhaust gas, do not consume oil, and the motor drive noise is small, easy to control, and can obtain good steady-state characteristics. As one of the three electric technologies of new energy vehicles, the motor controller is the nerve center connecting the motor and the battery, which is used to adjust the various performances of new energy vehicles. Undoubtedly, its safety issues must be taken seriously. Therefore, it is necessary to monitor the motor controller in real time, and timely warn and detect equipment failures. Among the many faults of the motor controller, the power device failure of the three-phase converter is the most common, and its consequences are also the most serious. It is usually divided into power device open circuit fault and power device short circuit fault. Among them, the short circuit fault can be solved by hardware circuit because of its short time and great harm; while the power device open circuit fault is not easy to be found, which may cause secondary system faults and cause greater losses.

At present, the open-circuit fault diagnosis methods for converter power devices mainly include two categories: current detection and voltage detection. The current detection method uses the current signal as a diagnostic variable, and comprehensively processes the current through coordinate transformation, signal processing, artificial intelligence or pattern recognition technology to realize the open-circuit fault diagnosis and positioning of the power device. Common current detection methods include current trajectory method, current vector feature analysis method, load current analysis method, etc. Usually, the current-based power device fault diagnosis method is easily affected by the system load and operating conditions, and the diagnosis cycle is long and the versatility is poor. The voltage diagnosis method is not affected by closed-loop control, is independent of the load and system operating conditions, has higher versatility and reliability, and has a shorter diagnosis time. However, some conventional voltage detection methods can only detect single-tube faults of switch tubes and require complex detection circuits. Therefore, a method for diagnosing open-circuit fault of power device of three-phase converter based on model predictive control is proposed. Firstly, the optimal switch state of the converter at time (k+1) is obtained by adopting model predictive control for the three-phase converter. Then, the switch state of the converter in actual application is obtained by detecting the voltage between the midpoint of each phase and the ground. Furthermore, according to the fault characteristics of the open-circuit power device of the converter, the difference of the switch state is compared, and the open-circuit fault flag signal _FTn of the power device is set. Finally, according to the states of different fault flag signals, it is judged whether the power device has an open-circuit fault, thereby realizing the diagnosis and location of the open-circuit fault of the power device of the three-phase converter.

Summary of the invention

Technical problem: In view of the existing open-circuit fault diagnosis method of converter power devices, a three-phase converter power device open-circuit fault diagnosis method based on model predictive control is proposed. This method does not require the addition of a large number of hardware circuits or the use of complex signal extraction circuits, and the signal processing algorithm is simple. It can quickly detect the open-circuit fault of the power device and achieve accurate positioning, and it has significant effects on single-tube, double-tube and multi-tube simultaneous faults.

To achieve the above technical objectives, the present invention adopts a method for diagnosing open-circuit faults of power devices in three-phase converters, comprising the following steps: configuring a model prediction control module to obtain the optimal switching state of the three-phase converter at the next moment at the current moment, step S1; when the next moment arrives, obtaining the current switching state of the three-phase converter according to the midpoint-to-ground voltage of each phase of the three-phase converter, step S2; configuring an open-circuit fault indication signal for each power device of the three-phase converter according to the fault characteristics of the power devices in the open-circuit state of the three-phase converter by comparing the optimal switching state and the current switching state, step S3; and judging the fault characteristics of the power device to which the open-circuit fault indication signal points, step S4.

Preferably, the step of configuring the model predictive control module to obtain the optimal switching state of the three-phase converter at the next moment is specifically: the phases of the three-phase converter are defined as phase a, phase b and phase c respectively, then at time k, the model predictive control is used for the three-phase converter to obtain the optimal switching state S _a1 S _b1 S _c1 of the converter at time k+1, which includes the following steps:

Step S11: Set the given DC side voltage The difference between the measured DC side voltage u dc and the actual measured DC side voltage u _dc is _input into the converter voltage outer loop PI regulator, and the d-axis current reference value is obtained according to formula (1):

In the formula, _kp and k _i are the proportional gain and integral gain of the voltage regulator respectively, and s represents a complex variable;

Step S12: using a phase-locked loop to obtain a three-phase converter grid voltage angle θ, and using a coordinate transformation module to transform the three-phase voltage e _abc and current i _abc into voltage and current u _dq and i _dq in a two-phase synchronous rotating coordinate system;

Step S13: discretize the converter current differential equation according to the first-order Euler equation shown in formula (2), and obtain the predicted value of the dq axis current of the three-phase converter at time k+1 according to formula (3):

Wherein, _Ts is the sampling period of the system; i _dq (k+1) represents the predicted value of the dq axis current at time k+1; i _dq (k) represents the sampled value of the dq axis current at time k; e _dq (k) represents the sampled value of the dq axis grid voltage at time k; u _dq (k) represents the sampled value of the dq axis output voltage on the AC side of the three-phase converter at time k;

Step S14: Set the reactive power reference value _iq ^* to 0, input the predicted value and reference value of the dq axis current at time k+1 into the value function module, respectively predict _idq (k+1) under the 8 switch states at time k+1, calculate the value function g _i according to formula (4), perform rolling optimization through the value function, and select the switch state that minimizes the value function as the optimal switch state S _a1 S _b1 S _c1 :

Where i = {1,…,8}.

Further preferably, the step of obtaining the current switching state S _a2 S _b2 S _c2 of the three-phase converter according to the midpoint-to-ground voltage of each phase of the converter is specifically as follows: define the two power devices included in each bridge arm of the three-phase converter as an upper tube and a lower tube, respectively, and then at time k, collect the midpoint-to-ground voltage of each phase: wherein, if the midpoint-to-ground voltage of the phase is u _dc , the current switching state of the phase is 1, and the upper tube of the phase is turned on; if the midpoint-to-ground voltage of the phase is 0, the current switching state of the phase is 0, and the lower tube of the phase is turned on, and the current switching states of each phase are arranged in phase sequence to form the current switching state S _a2 S _b2 S _c2 of the three-phase converter.

Further preferably, according to the fault characteristics of the power devices of the three-phase converter in the open circuit state, by comparing the optimal switch state and the current switch state, the step of configuring the open circuit fault indication signal _FTn for each power device of the three-phase converter is specifically: through the optimal switch state S _a1 S _b1 S _c1 and the current switch state S _a2 S _b2 S _c2 , independent power device open circuit fault indication signals FT ₁ , FT ₂ , FT ₃ , FT ₄ , FT ₅ , FT ₆ are established; if it is detected at time k+1 that the current switch state S _a2 S _b2 S _c2 of the three-phase converter is inconsistent with the optimal switch state S _a1 S _b1 S _c1 , the fault indication signal _FTn is set to 1 accordingly; if the current switch state S _a2 S _b2 S _c2 is the same as the optimal switch state S _a1 S _b1 S _c1 , the fault indication signal _FTn is set to 0.

Still further preferably, according to the open circuit fault indication signal, the step of determining the fault characteristic of the power device to which it points is specifically as follows: detecting whether the fault indication signal of each power device generates a jump from 0 to 1, determining whether the power device generates an open circuit fault, locating the fault, and outputting the open circuit fault information of the power device. Beneficial effects: The present invention is a three-phase converter power device open circuit fault diagnosis method based on model predictive control, which does not require the addition of a large number of hardware circuits or the use of complex signal extraction circuits, and the signal processing algorithm is simple and easy to implement. By detecting the switching state of the converter, the faulty power device can be quickly located, and it has significant effects on single-tube, double-tube and multi-tube simultaneous faults, and can effectively reduce the losses caused by the open circuit faults of the converter power devices in the motor controller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram showing an equivalent circuit structure corresponding to the three-phase converter according to the present invention;

FIG2 is a flow chart showing a control flow of a method for diagnosing an open circuit fault of a power device of a three-phase converter according to a preferred embodiment of the present invention;

FIG3 is a waveform diagram of the voltage and current of the power grid phase A of the converter under normal working mode;

FIG4 is a simulation waveform diagram of the grid-side current of phase A and the fault flag signal _FT1 when an open-circuit fault occurs in the power device VT1;

FIG5 is a simulation waveform diagram of the grid-side current of phase A and the fault signal _FT1 , and the grid-side current of phase B and the fault marking signal _FT4 when open-circuit faults occur simultaneously in VT1 and VT4;

FIG6 is a simulation waveform diagram of fault flag signals _FT1 to _FT6 when open circuit faults occur simultaneously in VT1, VT4, and VT6;

DETAILED DESCRIPTION

The present invention will be further described in detail below with reference to the accompanying drawings and by way of examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

The preferred embodiment of the present invention is proposed to solve the technical problem of open circuit failure of components in a three-phase converter in a motor controller in the prior art. The prior art has the following technical problems:

1) The current detection method is easily affected by load and operating conditions, has a long diagnosis cycle, and poor versatility;

2) The voltage detection method can only detect the failure of a single switch tube, and the detection circuit is complex, adding a large number of opinion circuits or using complex signal extraction circuits;

Therefore, the idea of solving the technical problem of the preferred embodiment of the present invention is to simplify the circuit and realize the accurate positioning of the single tube fault, especially the positioning when multiple tubes fail at the same time.

The idea of locating the fault is to configure a unique identification signal that identifies the fault status of the power device in each phase of the three-phase converter, forming a one-to-one correspondence between the power device and the identification signal. In this way, the working status of each power device at that moment can be obtained by judging the status of the identification signal. When an open circuit fault occurs, the device with the open circuit fault can be located according to the source of the identification signal.

A further question is how to obtain an identification signal that can identify the fault state of the device. Referring to FIG1 , FIG1 is a schematic diagram showing the equivalent circuit structure corresponding to the three-phase converter described in the present invention. As shown in FIG1 , the three-phase converter includes three bridge arms in parallel, and each bridge arm includes two power devices. In this embodiment, the power device is also a switch tube. The two switch tubes on each bridge arm are defined as an upper tube and a lower tube respectively according to the direction shown in FIG1 . Then, in the application state of the three-phase converter, one of the upper tube and the lower tube on each bridge arm is turned on. For ease of explanation, the switch tubes in FIG1 are marked as VT1 to VT6, wherein the two tubes on the first bridge arm are VT1 and VT2, the two tubes on the second bridge arm are VT3 and VT4, and the two tubes on the third bridge arm are VT5 and VT6.

For the current working state of a certain switch tube, its voltage to ground is measured. If the voltage to ground is not 0, the working state of the switch tube is considered to be on at this time, and its current working state _Sn is marked as 1 accordingly. If the voltage to ground is 0, the working state of another switch tube in the same bridge arm as the switch tube is considered to be on at this time, and the state of the non-conducting switch tube is marked as 0 accordingly. In this way, if the three phases in the three-phase converter are defined as phase a, phase b and phase _c respectively, then at time k, the current working state of the three-phase converter _{is SaSbSc} .

On the other hand, the switch tube of the three-phase converter will change its working state over time. Therefore, in a preferred embodiment of the present invention, a model predictive control is introduced to predict the optimal switch state of each switch tube when the next moment arrives at the current moment. Therefore, when the next moment arrives, the current working state of the three-phase converter is collected according to the aforementioned method and compared with the optimal switch state. If the two are consistent, it indicates that the switch tubes of each phase are working normally. If the two are inconsistent, it indicates that there is a switch tube with an open circuit fault.

As shown in FIG2 , a method for diagnosing an open circuit fault of a power device of a three-phase converter includes the following steps:

Step 1: Use model predictive control on the three-phase voltage source converter to obtain the optimal switching state S _a1 S _b1 S _c1 of the converter at time (k+1); specifically:

First, the given DC side voltage The difference between the measured DC side voltage u dc and the actual measured DC side voltage u _dc is _input into the converter voltage outer loop PI regulator, and the d-axis current reference value is obtained according to formula (1):

Where _kp and k _i are the proportional gain and integral gain of the voltage regulator, respectively, and s represents a complex variable.

Then, the phase-locked loop is used to obtain the voltage angle θ of the converter grid, and the three-phase voltage e _abc and current i _abc are converted into voltage and current u _dq and i _dq in a two-phase synchronous rotating coordinate system through a coordinate transformation module;

The converter current differential equation is discretized according to the first-order Euler equation shown in formula (2), and the predicted dq-axis current of the three-phase converter at time (k+1) is obtained according to formula (3):

Wherein, _Ts is the sampling period of the system; i _dq (k+1) represents the predicted value of the dq axis current at time k+1; i _dq (k) represents the sampled value of the dq axis current at time k; e _dq (k) represents the sampled value of the dq axis grid voltage at time k; u _dq (k) represents the sampled value of the dq axis output voltage on the AC side of the converter at time k.

Set the reactive power reference value _iq ^* to 0, input the predicted value and reference value of the dq axis current at time (k+1) into the value function module, predict _idq (k+1) under the 8 switch states at time (k+1) respectively, calculate the value function g _i according to formula (4), and finally perform rolling optimization through the value function to select the switch state that minimizes the value function as the optimal switch state S _a1 S _b1 S _c1 :

Where i = {1,…,8}.

Step 2: By detecting the midpoint-to-ground voltage of each phase, the actual switching state of the converter S _a2 S _b2 S _c2 is obtained. Specifically, by collecting the midpoint-to-ground voltage of each phase, a quick judgment is made: if the midpoint-to-ground voltage of the phase is u _dc , it indicates that the actual switching state of the phase is 1. On the contrary, if the midpoint-to-ground voltage of the phase is 0, it indicates that the actual switching state of the phase is 0;

Step 3: _According to the fault characteristics of the power device of the converter when it is open circuit, compare the difference _{between Sa1Sb1Sc1 and Sa2Sb2Sc2 ,} and set the power device open circuit fault flag signal _FTn , where n=1-6; specifically:

The changes in the system's switch state when open-circuit faults of power devices occur in different bridge arms of the three-phase voltage-source converter are analyzed and summarized in Table 1, where the open-circuit fault characteristics of each power device are independent of each other.

According to Table 2, the switching state of the converter actually applied under different power device open-circuit fault conditions is obtained. By comparing the optimal switching state S _a1 S _b1 S _c1 output by the converter prediction control and the switching state S _a2 S _b2 S _c2 actually applied by the converter, independent power device open-circuit fault flag signals FT ₁ , FT ₂ , FT ₃ , FT ₄ , FT ₅ , FT ₆ are established. If it is detected that the switching state S _a2 S _b2 S _c2 actually applied by the converter does not match the optimal switching state S _a1 S _b1 S _c1 , then according to Table 2, the corresponding fault flag signal FT _n will be set to 1; if S _a2 S _b2 S _c2 is the same as S _a1 S _b1 S _c1 , then the fault flag signal FT _n will be set to 0;

Taking phase A as an example, the intermediate variable _Ha is used to represent the difference between the actual switching state of phase A and the optimal switching state output by the converter model prediction control (H _a =S _a2 -S _a1 ). When i _a <0 and _Ha is -1, the fault flag signal FT ₁ will be set to 1, and FT ₁ will be set to 0 in other cases.

The open circuit fault flag signals FT ₁ and FT ₂ of the power device of phase A can be expressed by formula (5) and formula (6) as follows:

Similarly, the power device open circuit fault flag signals FT ₃ , FT ₄ , FT ₅ , FT ₆ of the B phase and the C phase can be obtained.

Table 1 Converter fault characteristics

Table 2 Optimal switching state of the converter under different fault conditions and the switching state in actual application

Step 4: Output the open circuit fault information of the power device of the three-phase converter according to the state of the fault flag signal _FTn ; specifically:

Detect whether the six fault flag signals have a jump from 0 to 1, determine whether the power device has an open circuit fault, locate the fault, and display the open circuit fault information of the power device through a display screen or a digital tube.

In order to verify the application effect of the open-circuit fault diagnosis method of the power device of the three-phase converter described in the present invention, the method described in the present invention is simulated and verified. First, the three-phase converter model predictive current control is simulated and verified. The voltage and current waveforms of the A-phase grid of the converter in the normal working mode are shown in Figure 3. It can be seen that the voltage and current are in phase in the steady state, and the model predictive control realizes the unity power factor rectification. Figure 4 shows the simulation waveform of the A-phase grid-side current and the fault flag signal FT ₁ when the power device VT1 has an open-circuit fault. It can be seen that at 0.1s, VT1 has an open-circuit fault, and the fault flag signal FT ₁ detects a jump from 0 to 1, generating VT1 fault information. When VT1 and VT4 have open-circuit faults at the same time, the system simulation waveform is shown in Figure 5. An open-circuit fault occurs at 0.1s. It can be seen that when a two-phase fault occurs, the phase current is severely distorted, and FT ₁ and FT ₄ can quickly generate fault information. When VT1, VT4, and VT6 have open-circuit faults at the same time, the system simulation waveform is shown in Figure 6. It can be seen that the corresponding fault flag signals _FT1 , _FT4 , and _FT6 can be quickly verified without affecting each other. The simulation results show that the open-circuit fault diagnosis method for power devices of three-phase converters proposed in the present invention is effective for single-tube, double-tube, and multi-tube faults at the same time.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (2)

1. The open-circuit fault diagnosis method for the three-phase converter power device is characterized by comprising the following steps of:

The step S1 of configuring a model prediction control module to predict the optimal switching state of the three-phase converter when the next moment comes at the current moment specifically comprises the following steps:

When each phase of the three-phase current transformer is defined as a phase a, a phase b and a phase c, model predictive control is adopted to the three-phase current transformer at the time k to obtain an optimal switching state S _a1S_b1S_c1 of the current transformer action at the time k+1, and the method comprises the following steps:

step S11: to give a DC side voltage The difference value e _n between the measured voltage u _dc and the actual measured voltage u _dc is input into the external ring PI regulator of the converter voltage, and the d-axis current reference value is obtained according to the formula (1)：

(1)

Wherein k _p and k _i are the proportional gain and the integral gain of the voltage regulator, respectively, and s represents a complex variable;

Step S12: the method comprises the steps of obtaining a three-phase converter power grid voltage angle theta by using a phase-locked loop, and converting three-phase voltage e _abc and current i _abc into voltage current u _dq、i_dq under a two-phase synchronous rotation coordinate system by using a coordinate conversion module;

Step S13: discretizing a current differential equation of the current transformer according to a first-order Euler equation shown in a formula (2), and obtaining a dq axis current predicted value of the three-phase current transformer at the moment k+1 according to a formula (3):

(2)

(3)

Wherein T _s is the sampling period of the system; i _dq (k+1) represents the predicted value of the dq-axis current at the time k+1, respectively; i _dq (k) represents the sampling value of the dq-axis current at the time of k, respectively; e _dq (k) respectively represents sampling values of the dq-axis grid voltage at the time k; u _dq (k) respectively represents sampling values of dq axis output voltage of the alternating current side of the three-phase converter at the moment k;

Step S14: setting reactive reference value For 0, inputting the dq axis current predicted value at the time of k+1 and the reference value into a cost function module, respectively predicting i _dq (k+1) under the action of 8 switch states at the time of k+1, calculating a cost function g _i according to a formula (4), performing rolling optimization through the cost function, and selecting a switch state with the minimum cost function as an optimal switch state S _a1S_b1S_c1:

(4)

where i= {1, …,8};

Step S2 of obtaining the current switching state S _a2S_b2S_c2 of the three-phase current transformer according to the voltage to the ground of each phase point of the three-phase current transformer when the next moment arrives;

According to the fault characteristics of the three-phase converter in the open state, the step S3 of configuring an open fault indication signal FT _n for each power device of the three-phase converter by comparing the optimal switch state with the current switch state is performed, specifically, the step S _a1S_b1S_c1 and the current switch state S _a2S_b2S_c2 are performed to establish the power device open fault indication signals FT ₁,FT₂,FT₃,FT₄,FT₅,FT₆ mutually independent of each other, if the moment k+1 is detected, the current switch state S _a2S_b2S_c2 of the three-phase converter is not in accordance with the optimal switch state S _a1S_b1S_c1, the fault indication signal FT _n is correspondingly set to 1, and if the current switch state S _a2S_b2S_c2 is the same as the optimal switch state S _a1S_b1S_c1, the fault indication signal FT _n is set to 0;

and step S4 of judging the fault characteristics of the pointed power devices according to the open circuit fault indication signals, namely detecting whether the fault indication signals of the power devices generate jump from 0 to 1, judging whether the power devices generate open circuit faults, positioning the faults and outputting open circuit fault information of the power devices.

2. The method for diagnosing an open circuit fault of a power device of a three-phase current transformer according to claim 1, wherein the step of obtaining the current switching state S _a2S_b2S_c2 of the three-phase current transformer according to the voltages to ground at each phase point of the current transformer comprises the steps of: specifically, two power devices included in each bridge arm of the three-phase converter are respectively an upper pipe and a lower pipe, and then at the moment k, the voltage to ground of each phase point is collected: wherein,

If the phase point-to-ground voltage is u _dc, the equivalent front switch state is 1, and the upper tube of the phase is conducted at this time;

If the phase point-to-ground voltage is 0, the equivalent front switch state is 0, at this time the phase is conducted with the down tube,

The current switching states of the phases are arranged according to a phase sequence to form a current switching state S _a2S_b2S_c2 of the three-phase current transformer.